1. Field of the Invention
The present invention relates to a medical device used to repair intertrochanteric fractures of the femur and a method for inserting and using the same.
2. Description of the Currently Available Technology
Current implants for the treatment of intertrochanteric (xe2x80x9cITxe2x80x9d) fractures consist of a variety of devices which are distinguished by three cardinal featuresxe2x80x94two of which are generally mechanical in nature and the third of which relates to the surgical procedure for implantation of the devices in a patient.
The femur is generally comprised of its head, which is ball-shaped and fits into the hip socket, its neck which is generally cylindrical in shape and extends from the head of the femur towards the shaft of the femur, the body or shaft of the femur which forms the major longitudinal axis of the femur, and an intermediate region which connects the shaft of the femur with the neck of the femur. This intermediate region is the trochanteric region and, very generally speaking, it holds the body of the femur and the neck of the femur at an angle of about 130 degrees relative to one another. This angle, often called the neck/shaft angle is not always precisely a 130 degree angle, but may vary considerably in each animal or human having a femur, but will generally be referred to hereinafter as a 130 degree angle for discussion purposes. Fractures in the trochanteric region of the femur are generally termed intertrochanteric or xe2x80x9cITxe2x80x9d fractures.
All orthopedic implants for the treatment of IT fractures of the femur must operate to hold the head of the femur at the above-described generally 130 degree angle relative to the body of the femur during healing of the fracture of the trochanteric and/or neck of the femur. All such orthopedic implants generally consist of three main elements. The first is a hip implant, also commonly referred to as a hip screw, which is screwed at one end into the head of the femur and extends therefrom to the body of the femur. The second is a stable platform affixed in some manner to the body of the femur. The third is a mechanism for affixing the hip screw and the stable platform to one another in order to hold the body of the femur and the head of the femur at the above-described generally 130 degree angle to one another while the fracture or fractures in the intervening region heals.
The three cardinal features which differentiate the presently available orthopedic implants are: 1) the type of stable platform employed by the implant (e.g., intramedullary or extramedullary); 2) the type of connection between the hip screw and the stable platform (e.g., rigid, dynamic or static plus dynamic); and 3) the surgical procedure, and more particularly, whether it is the hip screw or the stable platform that must be first implanted in the patient.
With regard to the first cardinal feature, there are two types of stable platforms which can be affixed or otherwise associated with the body of the femurxe2x80x94intramedullary and extramedullary. Extramedullary platforms typically employ one or more plates affixed to the outside of the body of the femur with screws which extend generally transverse to the femur""s longitudinal axis into the body of the femur to attach the plate to the body of the femur. The hip screw and plate are affixed to one another to hold the head of the femur and the body of the femur at the above-described generally 130 degree angle during the healing process. Extramedullary platforms of this type are particularly useful for nondisplaced or minimally displaced IT fractures.
Intramedullary platforms typically employ an intramedullary nail (IM nail) which is generally a metal rod or tube which is inserted from the top of the femur through the trochanteric region into the hollow core of the body of the femur (known as the intramedullary cavity). The intramedullary nail extends along a portion of the body of the femur, and may extend from the trochanteric region of the femur through nearly all of the body of the femur. The intramedullary nail is generally affixed at its end opposite the end implanted in the trochanteric region (e.g., that portion of the intramedullary nail nearest the patella) to the shaft of the femur with screws inserted transverse to the longitudinal axis of the shaft of the femur through the femur and through the intramedullary nail. The hip screw is positioned generally transverse to the intramedullary nail""s longitudinal axis into the head of the femur. The intramedullary nail and hip screw are affixed to one another as explained below, to prevent relative motion in order to provide the stabilization of the body of the femur and the head of the femur at the above described generally 130 degree angle during the healing process.
As between intramedullary platforms and extramedullary platforms, intramedullary platforms are generally more desirable because the moment arm between the head of the femur and the intramedullary nail is less than that of the moment arm of extramedullary platforms where the moment arm extends between the head of the femur and the extramedullary plate attached to the outside of the femur. Thus, the moment arm mechanical forces on the intramedullary implant are lower and it is therefore less likely to experience a mechanical failure. Intramedullary platforms are also desirable because they generally involve a less invasive surgical exposure for implantation. In other words, rather than having to make a surgical incision along a substantial portion of the length of the femur sufficient to permit the surgeon to insert the plate of the extramedullary platform and attach it to the outside of the body of the femur, the intramedullary platform permits the surgeon to simply make a small incision at the top of the femur to insert the intramedullary nail and a small incision on the side of the femur to insert the hip screw.
With regard to the second cardinal feature, the type of connection between the hip screw and the stable platform differentiates presently available orthopedic implants. Such connections may be rigid, dynamic or xe2x80x9cstatic plus dynamic.xe2x80x9d
Bone compression occurs during the healing process. Bone compression or simply compression, refers here to the process in which bones held together during healing collapse into one another during the healing process to provide a smaller overall dimension than that provided when the fragments were first placed contiguous to one another during the surgery conducted to set the broken bone. Uncontrolled compression is undesirable, but controlled compression is desirable as it permits the fractured bone to heal along desired or required compression paths.
Rigid connections permit no movement in any direction between the stable platform and the hip screw, and are therefor unable to accommodate bone compression that may occur during the healing process.
Dynamic connections permit some movement between the stable platform and the hip screw during the healing process. More particularly, where for example the femur is a human femur and the patient is viewed from a standing position, dynamic connections permit the stable platform to move closer to or further away from the head of the femur along the longitudinal axis of the hip screw, but do not permit vertical movement of the stable platform relative to the longitudinal axis of the hip screw. Dynamic connections can accommodate bone compression, and allow the hip screw to guide the fracture to its most stable position during the healing process without further surgical intervention, but do not provide a post-operative compressive force along the longitudinal axis of the hip screw to urge the stable platform towards the head of the femur, which may be desirable to stabilize the fracture.
Static plus dynamic compression devices also provide such guidance, but permit the surgeon to stabilize the fracture intraoperatively by applying compression forces on the fracture and then allow further dynamic compression during the healing phase.
With regard to the third cardinal feature, the order in which the hip screw and the stable platform are to be surgically implanted differentiates presently available orthopedic implants. More particularly, the design of the orthopedic implant determines the sequence of implantation of the hip screw and the stable platform (e.g., intramedullary nail). In certain intramedullary platforms the hip screw is first inserted, and the stable platform (e.g., intramedullary nail) is then inserted through the hip screw. This type of platform may be referred to as the xe2x80x9chip screw-firstxe2x80x9d type. In other types, the stable platform (e.g., intramedullary nail) is first inserted followed by insertion of the hip screw. These types may be referred to as xe2x80x9cstable platform-firstxe2x80x9d type.
Hip screw-first designs are desirable because they have a tendency to stabilize the fracture with the hip screw. Subsequent insertion of the stable platform, particularly where the stable platform is an intramedullary nail, is less likely to destabilize or produce unwanted movement of the bone fragments or alignment of the bone fragments. In contrast, stable platform-first designs, particularly where the stable platform is an intramedullary nail, have the potential of causing unwanted distortion of the fracture, unwanted movement of the bone fragments and/or unwanted misalignment of the bone fragments during insertion of the intramedullary nail, which may not and often cannot be corrected upon insertion of the hip screw through the intramedullary nail.
While there are presently available many platforms for the stabilization of the femur to provide for healing of the same for both IT and other femur fractures, there does not exist a platform which: is intramedullary; is capable of providing static plus dynamic compression; and which is of the hip screw-first design, which would therefore combine the best attributes of each into a single orthopedic implant. A need exists in the art for such an intramedullary platform.
It is an object of the present invention to provide a novel orthopedic implant which is minimally invasive, allows custom fitting of an implant to the dimensions of the femur of a patient, allows for static compression to be applied at the time of surgery as well as allowing for dynamic controlled collapse of the fracture during the healing process and which allows fixation to the shaft of the femur by an intramedullary nail. It is an object of the present invention to provide an orthopedic implant which is intramedullary; is capable of providing static plus dynamic compression; and which is of the hip screw implantation-first design.
These and other objects are obtained with the orthopedic implant of the present invention which includes in cooperation a hip screw, a gliding mechanism, an intramedullary nail, and a compression screw.
The hip screw includes an externally threaded portion for threadable insertion into the head of the femur and a hollow barrel portion, the barrel portion having a pair of opposed slots provided therein along the longitudinal axis of the hip screw. In one embodiment, the hip screw is a hollow tube that tapers from a first diameter to a smaller diameter, the smaller diameter portion having an externally threaded portion to act as a bone screw for insertion into the head of the femur, the larger diameter portion having the slots provided therein. The hollow tube further includes internal or female threads within the barrel portion near the end of the hip screw opposite the bone screw for threadably engaging the compression screw.
The gliding mechanism is generally cylindrical and is retained within the barrel portion of the hip screw with a slidable fit and has a throughhole therethrough transverse of the longitudinal axis of the hip screw. The throughhole is of a diameter which allows a slidable fit with the outside diameter of an intramedullary nail. The throughhole of the gliding mechanism aligns with the slots in the barrel portion of the hip screw to permit the intramedullary nail to pass through the first slot of the barrel portion of the hip screw, through the throughhole of the gliding mechanism and to pass through the second slot of the barrel portion of the intramedullary nail as the intramedullary nail is inserted into the femur through the hip screw and gliding mechanism, whereupon the intramedullary nail is affixed to the gliding mechanism to prevent relative motion between the gliding mechanism and the intramedullary nail.
Upon securing the gliding mechanism to the intramedullary nail, in turn the hip screw and the intramedullary nail are affixed to one another, but due to the slidable fit of the gliding mechanism within the barrel of the hip screw and due to the slots in the hip screw, movement of the gliding mechanism/intramedullary nail assembly along the longitudinal axis of the hip screw can occur as the gliding mechanism glides within the barrel portion of the hip screw.
The internally threaded portion of the barrel portion of the hip screw threadably engages the compression screw, which compression screw is of sufficient length so as to contact the gliding mechanism while the compression screw is still threadably engaged with the internal threads of the barrel portion of the hip screw. Rotating the compression screw further and further into the barrel portion of the hip screw causes the compression screw to urge the gliding mechanism along the longitudinal axis of the hip screw in the direction of the head of the femur, which in turn forces the intramedullary nail in the same direction. Such movement of the intramedullary nail is accommodated by the opposed slots in the barrel portion of the hip screw. As gliding mechanism/intramedullary nail assembly is urged towards the head of the femur, the head of the femur and the body of the femur are caused to be urged toward one another, allowing the surgeon to provide whatever static intra operative compressive force between the body of the femur and the head of the femur is deemed medically necessary. However, as the bone fragments collapse during the healing process, the surgeon can re-operate and rotate the compression screw to provide more compressive force if deemed medically necessary.
In an alternative embodiment of the present invention, the gliding mechanism may be formed of two portions which are joined about the intramedullary nail. While this embodiment introduces additional pieces, it also introduces flexibility in that unlike the above-described embodiment having a throughhole in the gliding mechanism which establishes a fixed angle between the intramedullary nail with respect to the hip screw, the two part embodiment of the gliding mechanism permits any angle between the intramedullary nail and the hip screw, which angle is maintained and secured when the two portions of the gliding mechanism are joined about the intramedullary nail.
The process for the insertion of the orthopedic implant of the present invention is also novel and forms a part of the present invention.